Using a powerful approach called GCTA, King’s College London researchers Maciej Trzaskowski and colleagues found no evidence that genetics can explain differences in children’s behavioural and conduct difficulties.

First some background. ‘Missing heritability‘ refers to the fact that genetics has mostly failed to find common genetic variants that are associated with ‘complex traits’ like personality, mental disorer and intelligence.

This is surprising because these traits are largely heritable – meaning that they run in families, and that identical twins (with all their DNA in common) tend to be more similar than non-identical ones (with only half). But if they’re heritable then, by definition, there must be genes behind that.

But with a few minor exceptions, over a decade of studies drew blanks. Hence the heritability is missing in our DNA, unaccounted for.

Yet geneticists finally struck gold – or seemed to – with a new technique called genome-wide complex trait analysis (GCTA). Instead of looking at each variant individually, GCTA quantifies how genetically similar any two people are as a whole.

GCTA has shown that the more genetically similar people are, the more similar they tend to be in terms of complex traits. Hooray – the missing heritability is… well, it’s still missing, but at least we know it’s out there, in small pieces scattered across the genome.

But this good news only applies to some complex traits, according to Trzaskowski et al. It doesn’t hold for child behaviour.

In the TEDS sample of British twins, the authors conducted a simultaneous twin and GCTA study. During childhood these twins were assessed for IQ, height, weight, and a range of ‘behaviour problems’ including symptoms of autism, hyperactivity, psychopathy, conduct disorder and more.

The results of the twin study said that all of the traits were moderately heritable (roughly 0.5 on the scale of 0 to 1).

But while GCTA confirmed a large genetic influence on the intelligence traits, height and weight, it found no genetic influence on the behaviour measures:

The difference between the two sets of traits is stark. The same picture was seen whether it was parents (shown here), teachers, or the children themselves rating their behavioural symptoms.

So, some of the missing heritabilities have been located (if not pinned down), but others are more missing than ever.

Trzaskowski call it a “new kind of missing heritability” but I wonder if the name “mystery heritability” is more appropriate in relation to these behavioural problems. What’s going on?

The authors say that GCTA can only detect additive genetic effects, and can’t detect nonlinear interactions between genes. But the trouble is, the twin data just aren’t consistent with the idea that nonadditive effects explain any of these traits.

However, Trzaskowski then suggest that the results make sense if we assume that twin studies substantially overestimate the heritability of behaviour problems (but not intelligence).

This might be because behaviour problems are just questionnaire ratings of traits, which are essentially subjective and prone to bias (e.g. by parents who assume that their identical twins ‘must be identical’ and rate them as such), while intelligence tests, although not perfect, are less easily fudged.

This account does leave room for some genuinely heritability, but only a little.

But have they been shown to be valid when comparing twin pairs? Because it might be that they are fine when used normally, but when it comes to twins, people do not rate them in the same way as they otherwise do (i.e. they exaggerate MZ similarity)

Something of a stretch admittedly, but it’s hard to see a better explanation of these data…

I would also think the rater bias criticism would less applicable to the self-reports by the twins themselves.

http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

OK, good find – I hadn’t seen that paper. But self-ratings can’t be taken to be bias-resistant.

Many identical twins are aware of their “identity” from a young age, go around doing everything together and so on. They might see themselves as even more similar than they really are.

http://www.twitter.com/jdottan JT

I agree that self-report isn’t bias-resistant, but that’s why they are looking across different reporters. I guess what I’m getting at is that I don’t think the different forms of bias across reports are fully accounting for the discrepancy in heritability; but I don’t think I have any better ideas.

http://www.jugarjugar.net/ Jugar Jugar

I think a prerequisite is the habitat and behavior of parents affects children the most. In the early years age group, the kids sure like the paper in the morning, it will be influenced by the teachings and behavior of parents as well as those around them. Genetic problems are not sure

Mollijoy Carter

I think anything can be learned, then un learned. It is all about “How” the brain is wired, Then, how the environment And behavior influence, what is already there….

radonx

I have direct experience as an identical twin. Scientists investigate and argue that genetically identical twins knows – behavior is a complex phenomenon determined by many circumstances from which the genetic determination has only an indirect effect only to the condition that the behavior was manifested. But the character (nature, ethos), that’s what affects the decision may be different to antagonistic, to the eyes of the neighborhood form a clear two distinct individuality. How so? Genes are identical, family and education in school are the same. The same circle of friends, the same circumstances and events … If I use logic, I have no other explanation than that in each of the two cells after division as a basis for future two bodies entered something like two distinctive characters.

http://blogs.discovermagazine.com Donald Klein

The absence of evidence is not evidence of absence.

http://PolyKhromeGames.blogspot.com/ Brian Lockett

It’s not the delimiter of possibility, either.

Ruben C. Arslan

Recent rare variants and new mutations are, I think, strong candidates to account for part of the gap between twin-derived heritability estimates and GCTA estimates, especially for autistic symptoms (Iossifov et al. 2012); I think we know less about this for other behaviour problems. I was surprised that the authors only hint at this by including rare variants in a list of “could-bes” even though the explanation they could test, nonadditive variation, comes up short.

Emmanuelle Baudry

Indeed, a simple explanation, consistent with recent studies on the genetic architecture of autism, would be that whereas size or IQ are influenced by numerous common variants with very small effects, behavioral problems like autism are influenced by rare recent variants, sometimes with strong effects.

The authors suggestion that nonadditive genetic influence might explain the discrepancy between twin and GCTA estimates does not seem very convincing.

When you see that you (every one) is genetically engineered, you see the life force, propelling force of your every action.All your seeing, listening, speaking, touching, thinking is a chemical process. Can
not I change myself? This is a thought triggered as a chemical process. When you see that it is a trigger, you see the propelling force, the life force, self-sustained.
‘You’ see yourself as the total field of Existence.
The same force is propelling all the movements. See any micro movement to see the force.https://sites.google.com/site/yvchawla/happenings-around-and-fundamentals/thelifeforce

andrew oh-willeke

I am inclined to think that the behavioral syndromes listed are the product of fairly elaborate systems of genes, and that a failure in any one component of that system (including many novel mutations shares only by a handful of close relatives) will cause that syndrome.

Suppose autism is genetic but that there are three hundred target sites where a mutation could cause it, and that different mutations at the same target site can each cause autism. There might be a thousand genetically distinct causes of autisms that all muck up the same overall neurological development system and cause the same syndrome. But, because each autism sufferer has a different genetic source, the GCTA mechanism which is looking for repetition of the same genetic source for multiple cases of the same disorder would miss the genetic cause.

Moreover, in any syndrome where risk is associated with advanced paternal age, which normally indicates a significant contribution of novel genetic mutations to the syndrome, of which autism is just one example, you would expect GCTA to have a hard time discerning the genetic source of the syndrome.

Bad Kids Go To Hell

Our research shows: Bad Parenting = Bad Kids Go to Hell.

jimbow

what about problem men with double Y’s? they as a hole are big and trouble makers.

Classical twin study design has been the greatest obstacle to understanding how genes and environment interact. In autism, classical twin studies cannot control for the high rate of de novo gene mutations, therefore, the heritability estimates in the autism twin studies are vastly inflated.

“But if they’re heritable then, by definition, there must be genes behind that.”

Technically, this is true, but because of the design used by twin studies this inference can easily be confounded. What if genetic factors present at birth influence environmental factors that a person is exposed to across the lifespan, leading to changes in how these genes are expressed and subsequent behaviour? Because individuals with more similar genes are likely to have more similar gene-by-environment interactive effects of this sort, the greater similarity of twins on complex traits may be partly accounted for in terms of non-heritable factors.

The twin study design and the typical models used to analyze such data assume that this is not an issue, but it’s unclear that this assumption will hold for complex traits.

Lah99

Study leaves out epigenetics and noncoding RNA regulatory effect.

fungus_Amongus

…so what really is the big deal here? is there some reason that science is hell-bent on needing child behavior to be have a deep genetic component?

if the data shows what everyone seemed to want to be there *not* to be there, well then damn…move on to different theories!

it’s my guess that early childhood experiences are the crucial driving factor behind behavior issues…perhaps even one seemingly unimportant event (to the parent at least) can and does scar a child (and adult) in ways we just don’t totally understand yet.

John McIntire

there’s definitely something to childhood experiences shaping people, but i think the “big deal” is that one set of data (e.g., twin studies) show a heritability component, but this is harder to find in the genetics than one would have thought….is it because the twin studies are overestimates, or because we have an incomplete understanding of how genetics ultimately ends up effecting behavior? seems an important question

fungus_Amongus

couldn’t agree more…”debugging” the brain is probably the most important scientific inquiry running these day, imho at least…

this is why i’m so interested in the fMRI stuff going on now and have hope that as this technology matures, real progress can be made in understanding how all of our “wetware” is really working so honest-to-goodness therapies can be developed that we will be able to “see” actually work, where it counts, in the brain.

Renee Sanford

child behavior in identical twin is very similar considering they share a lot of the same traits and heredity. traits and behavioral issues are hereditary.

http://blogs.discovermagazine.com Ron Hansing

It is not the
genes… but epigenetics… the turning off and on of genes. For example, only
50% of identical twins will develop Schizophrenia. Research has shown that in
mice, poor nurturing mothers produce mice with a much higher degree response to
stress… Yet when one puts these mice with a nurturing mother, their stress
level is less.

All the cells in
the body have the same genes… In the liver,
all the genes are turned off except for the genes that the liver codes
for. Some genes have a very strong lock
of which genes will be turned on and off… others such as in behavior issues,
have a much weaker lock and various chemicals, emotional trauma can tune the
genes on or off to present a phenotype… And reprograming and therapy can remap
the neural network… ie, turn on or off
the gene to change the phenotype.

Well, at least
that is my hypothesis… that some research
seems to suggest. The 20th
century will be the century of neuro
physiology. The brains is plastic,
malleable and is the most active organ in our bodies… Much research of course
is still needed but I predict great advancement since we now know that the field of epigenetics is the next big
challenge. Yes. Maybe I’m just way off
base… but who knows… research will made this clearer in the future.

Ron hansing
10.10.13

http://blogs.discovermagazine.com David Doss

Like several others, I think the missing heritability will be found in epigenetics.

Only idiot scientists would think genes have anything to do with behavior problems of children. Ask any parent, kids go wacko after sugary food, drinks, and snacks.

http://assistantvillageidiot.blogspot.com Assistant Village idiot

No they don’t. It has been blind-tested repeatedly. It’s a myth. Parents see what is not there. High sugar times are also high social-stimulus times, such as parties and gatherings. That’s only one confounding factor.

I’m a father of five, before you dismiss my claims quickly.

As for the other comments, there is a lot of faith being placed in epigenetics. Maybe.

I wonder if you have considered the impact of visual problems. There is plenty of research indicating slight visual weaknesses in a broad swathe of children (premature, those with squints or other binocular instabilities (even when cosmetically rectified), those on medication etc.).

These children can have 20:20 vision but are at a
massive disadvantage when trying to learn symbols, because they have not seen the elements of shape well enough at an early stage. (They can be taught later!)

The strain of visual fatigue and classroom disadvantage almost inevitably leads to behavioural problems. There are simple things that educators
could do to ease the strain i.e. printing & writing larger and cutting out copying from the board. They could let students write larger and bolder so
that they could ‘see’ their work clearly, but unfortunately tradition seems to dictate that teachers require students to write between narrow lines
or within small space/boxes too early.

I am an experienced researcher and have tested this hypothesis of poor symbol knowledge repeatedly through years of teaching dyslexics, autistics, ADHD,
hearing or visually-impaired & all the other types of students who tend to fail.

I specialise in improving dyscalculics, and find
that if I take a student from learning elementary maths symbols through place value, maths notation and on to algebra they improve. They have
learned a succinct symbolic language which allows them to ‘read & write’ maths. The burden on working memory is reduced, and they can develop inference and deduction because they can lay out the problem and see it.

In tandem they begin to understand why they failed and made ‘silly’ mistakes. They forgive themselves for failure and discard shame and anxiety.

Of course getting better at Maths is an added boost for esteem, as it is an elite subject, and so many other subjects hinge on it.

Needless to say I enjoy my work.

(Incidentally as a twin I found Maths easy at school, while my equally intelligent brother was pitiful. I am myopic, he has excellent vision.)

In twins there is almost always one more dominant than the other. Surely the adaption to dominance and submissiveness must play a role in how other personality aspects develop.

abinico

Sugar can reduce an otherwise smart kid into a drooling, babbling idiot. I have seen it many times. I used to teach martial arts to kids and would easily pick out the ones that had a sugary drink during the break. The effects are dramatic.

http://assistantvillageidiot.blogspot.com Assistant Village idiot

Submit that to testing, if you dare. Your “easily” will go down in flames as soon as there are yardsticks.

I get the impression you didn’t take much math in school.

abinico

And a final word on genes. Genes do only one thing – that’s adapt to their environment. Aggression is more likely to come from several genes, and can indeed be a passed trait thru natural selection. Though in humans natural selection stopped working ages ago and today’s aggression is more likely from a number of exogenous factors.

Said it before and will say it again – HFCS drives kids wacky. Period. Only a sugar industry shill would deny this.

Lauren

We just learned about this is my psych 101 class. From what I understand, a person’s phenotype can take multiple forms. Those are the different alleles of a gene. The environment can influence a gene throughout a person’s life and take different forms. This is why the “Nature vs Nurture” theory is no longer a big controversy in psychology. Just because a trait appears a particular way at one point in their life, does not mean it will always be that way.

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About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.